AC Compressor

This procedure covers the removal and replacement of the AC compressor on a 2007 Ram 3500 with the 5.9L Cummins diesel engine, including refrigerant recovery, compressor replacement, and system recharge.

Warnings

Tools required

Parts

• AC compressor assembly × 1 — Verify Sanden-style compressor for 5.9L Cummins
• AC line O-rings × 4 — Use OEM specification
• Serpentine belt × 1 — Recommend replacement if worn
• PAG46 compressor oil × 1 — 8-10 oz capacity

Fluids

• R-134a refrigerant

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow engine to cool completely for at least 2 hours
3. Disconnect negative battery cable
4. Verify AC system pressure using manifold gauges before recovery
5. Connect AC recovery machine and recover all refrigerant from system according to machine instructions
6. Measure and record amount of oil recovered to determine replacement quantity

Procedure

1. 1

   Remove serpentine belt
   Using a serpentine belt tool or the appropriate socket on the tensioner pulley bolt, rotate the belt tensioner to release tension (verify direction against the underhood belt routing diagram). Remove the serpentine belt from all pulleys including the AC compressor pulley. Inspect belt for wear, cracks, or glazing and replace if necessary.
2. 2

   Disconnect AC compressor electrical connector
   Locate the AC compressor clutch electrical connector on the front of the compressor. Press the release tab and disconnect the harness connector from the compressor clutch coil.
3. 3

   Disconnect AC suction and discharge lines
   Locate the AC line fittings on the rear of the compressor. Verify the AC line connection type: many 5.9L Cummins compressors use a single manifold block secured by one central bolt rather than individual flare fittings. If a manifold block is used, remove the retaining bolt and separate the block. If individual fittings are used, carefully loosen and remove both the suction line (larger diameter) and discharge line (smaller diameter) fittings with a crowfoot or flare nut wrench. Cap all open fittings immediately to prevent contamination. Remove and discard all O-rings from the fittings.
   ⚠Even after recovery, residual refrigerant may remain in lines. Work in well-ventilated area and avoid breathing any released refrigerant.
4. 4

   Remove AC compressor mounting bolts
   The compressor is mounted to a bracket on the engine with mounting bolts. Verify the exact bolt count and socket size against factory service data, then remove all compressor mounting bolts. Support the compressor while removing the final bolt to prevent it from falling.
5. 5

   Remove AC compressor from vehicle
   Carefully maneuver the compressor out of the engine bay. Due to the tight clearance around the Cummins engine, you may need to tilt and rotate the compressor to clear the radiator support and intercooler piping. Work slowly to avoid damaging surrounding components.
6. 6

   Drain and measure compressor oil
   Drain the old compressor completely by rotating it and pouring oil out through one of the ports. Measure the total oil removed from both the recovered refrigerant and the old compressor. Add fresh PAG oil of the OEM-specified viscosity to the new compressor. Balance the oil charge to match the amount removed plus any factory-specified pre-charge, and verify total system oil capacity against the underhood/service label.
7. 7

   Install new AC compressor
   Maneuver the new compressor into position on the mounting bracket, reversing the removal path. Align all three mounting bolt holes with the bracket. Start all three mounting bolts by hand before tightening any of them.
8. 8

   Torque compressor mounting bolts
   Using a torque wrench, tighten the AC compressor mounting bolts evenly to the factory-specified torque (verify count, socket size, and torque value against factory service data).
   Torque spec

   AC Compressor Mounting Bolts25 Nm (18 lb-ft)
9. 9

   Install new O-rings and connect AC lines
   Install new O-rings onto both the suction and discharge line fittings. Lightly coat the O-rings with fresh PAG oil. Thread both fittings into the compressor ports by hand to ensure proper alignment and prevent cross-threading. Once hand-tight, use a crowfoot or flare nut wrench and torque wrench to tighten the fittings.
   ⚠Do not over-torque AC line fittings as this can damage the O-rings and cause leaks. Use a crowfoot wrench with torque wrench for accurate measurement.
   Torque spec

   AC Line Fittings20 Nm (15 lb-ft)
10. 10

    Reconnect compressor electrical connector
    Plug the electrical connector back into the AC compressor clutch coil until it clicks into place. Ensure the connector is fully seated and the locking tab engages.
11. 11

    Reinstall serpentine belt
    Route the serpentine belt around all pulleys according to the belt routing diagram on the fan shroud or underhood label. Rotate the belt tensioner clockwise and slip the belt onto the final pulley. Release the tensioner slowly to apply proper tension to the belt.
12. 12

    Vacuum test AC system
    Reconnect the battery. Connect the AC vacuum pump and manifold gauges to the service ports. Pull a vacuum on the system for at least 45 minutes, then close the valves and monitor for 30 minutes. The system should hold vacuum without any pressure rise, indicating no leaks.
    ⚠If vacuum does not hold steady, there is a leak in the system. Do not proceed with recharging until leak is located and repaired.
13. 13

    Recharge AC system
    With the system under vacuum, connect the refrigerant supply to the low-side service port. Start the engine and turn on the AC to maximum cold with blower on high. Slowly charge the system with R-134a refrigerant to the exact quantity listed on the underhood specification label for this vehicle. Use a refrigerant scale to ensure accurate charging. Monitor pressures on the manifold gauges during charging.

Reassembly

1. Verify all AC line connections are secure and properly torqued
2. Ensure serpentine belt is properly seated on all pulleys with correct tension
3. Confirm electrical connector is fully engaged on compressor clutch

Verification

• Start the engine and turn AC to maximum cold. Verify compressor clutch engages and you hear/see the clutch and pulley spinning together
• Check low-side pressure: should be approximately 25-35 PSI with ambient temperature at 75-80°F
• Check high-side pressure: should be approximately 200-250 PSI with ambient temperature at 75-80°F
• Verify cold air from vents reaches at least 40-45°F colder than ambient temperature
• Inspect all AC line connections for signs of oil leakage which would indicate refrigerant loss
• Allow system to run for 10-15 minutes and recheck pressures to ensure they stabilize within normal range
• Use an electronic leak detector around all fittings to verify no refrigerant leaks

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